Ecological Research (2003) 18, 165–175 Blackwell Science, LtdOxford, UK ERE Ecological Research 0912-38142003 Ecological Society of Japan 182March 2003 544 Carbon budget of a hinoki stand S. Adu-Bredu and A. Hagihara 10.1046/j.0912-3814.2002.00544.x Original Article165175BEES SGML *Author to whom correspondence should be addressed. Present address: Plantation Production Division, Forestry Research Institute of Ghana, University PO Box 63, Kumasi, Ghana. Email: sa_bredu@yahoo.com Long-term carbon budget of the above-ground parts of a young hinoki cypress (Chamaecyparis obtusa) stand STEPHEN ADU-BREDU 1 * AND AKIO HAGIHARA 2 1 Forest Ecology and Physiology Laboratory, Forest Sciences Division, School of Agricultural Sciences, Nagoya University, Nagoya 464-8601, Japan and 2 Laboratory of Ecology and Systematic, Faculty of Science, University of the Ryukyus, Okinawa 903-0213, Japan The carbon budget of the above-ground parts of a young hinoki ( Chamaecyparis obtusa) stand was analyzed over a 4-year period to evaluate trends in changes in carbon use efficiency and growth conversion (biosynthetic) efficiency with stand development. Litter production of the stand was estimated from the stem cross-sectional area at the crown base. A biomass increment was estimated using the stem volume of individual trees in the stand, measured at monthly intervals. Net production, estimated from litter production and the biomass increment, was 7.40, 8.44, 8.45 and 8.29 Mg C ha -1 year -1 for Years I–IV, respectively. The respiration rate of the entire above-ground parts of selected sample trees were measured at monthly intervals using the enclosed whole-tree method. The Q 10 value of respiration decreased with increasing air temperature. Respiration rate was partitioned into growth and maintenance components using a two-component functional model. The maintenance respiration coefficient increased in the following order: winter, spring, autumn and summer. The maintenance respiration coefficient also decreased with either stand development or age for all seasons. The growth respiration coefficient, which did not vary with stand development, was 0.69 ± 0.08 (mean ± SE), 0.61 ± 0.03, 0.54 ± 0.03 and 0.67 ± 0.07 g C g -1 C for winter, spring, summer and autumn, respectively. The growth conversion efficiency of the stand was 0.76, 0.72, 0.72 and 0.75 for Years I–IV, respectively. Carbon use efficiency was estimated to be 0.58, 0.57, 0.54 and 0.53 for Years I–IV, respectively. The hypothesis that respiration reduces productivity in old stands could not be validated for this hinoki stand. Key words: carbon use efficiency; growth conversion efficiency; hinoki; growth respiration coefficient; maintenance respiration coefficient; net production. INTRODUCTION Plant growth and productivity are normally con- sidered in terms of carbon balance because carbon plays a dominant role in plants, although other elements also play essential roles. Carbon balance and biomass accumulation of a forest stand can be fully accounted for only when all the gains and loses of carbon are considered (Amthor & McCree 1990). Photosynthesis is the primary physiological process responsible for the acquisition of carbon by a plant. After respiration has been accounted for, the net primary production is used to build up organic matter, part of which is lost as dead mate- rial (litter) or grazed during the course of the year, with the remaining yield going into existing bio- mass. When deriving carbon budgets and validat- ing models, knowledge of the size of the respiratory fluxes is important (Ryan et al. 1996). Respiration must be compared with the rest of the carbon budget to analyze its role in forest produc- tivity. It is also important to clarify how the pro- portion of assimilation used for production (i.e. carbon use efficiency) varies with stand develop- ment. The quantitative significance of respiration to a plant’s carbon balance is expressed by carbon Received 31 October 2001. Accepted 25 July 2002.